Technical Field
The invention relates to optical devices and methods for making and using optical devices.
Related Art
This section introduces aspects that may be help to facilitate a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
One type of optical coupler is an optical grating. An optical grating can be configured as a surface optical coupler that optically couples a near end of an optical fiber, which is facing the surface, to an optical waveguide, which extends along the surface. Often, such a configuration of an optical coupler is largely tolerant to the alignment between the near end of the optical fiber and the optical grating. Also, such a configuration of an optical coupler can be configured to substantially only couple to selected optical propagation mode(s) of the optical fiber.
Nevertheless, such an optical coupler often has high optical losses. For example, a substantial part of the light emitted by the near end of an optical fiber may pass through a thin optical grating and be lost. To reduce such losses, the back-sides of some optical gratings are coated with an optical reflector. Then, light passing through the optical grating may be reflected back to the optical grating, thereby increasing the efficiency of the optical coupling of the near end of the optical fiber to the optical grating.
Forming an optical reflector on the backside of an optical grating is typically a multi-step process. Some such processes include performing an anisotropic back-side etch of a planar substrate on whose front surface the optical grating is formed. The anisotropic back-side etch forms an opening in the planar substrate. The opening provides access so that an optical reflector can be deposited along a back-side of the optical grating. The formation of the opening in the back-side of a planar substrate may also include thinning the substrate to simplify the later anisotropic back-side etch of the substrate.